1. Field of the Invention
The present invention relates to a cutting tool made of a surface-coated carbide alloy (hereinafter referred to as a coated cemented carbide tool) which causes neither peeling nor chipping (microchipping) in a wear-resistant coating layer when various types of steel and cast iron are interruptedly cut under deep cutting conditions such as thick depth-of-cut and high feed where high mechanical and thermal impacts are applied, because the wear-resistant coating layer is superior in adhesion to the surface of a tungsten carbide-based carbide alloy substrate (hereinafter referred to as a cemented carbide substrate) and is also superior in resistance against chipping, thus exhibiting excellent wear resistance for a long period of time.
2. Description of the Related Art
In general, cutting tools include, for example, a throw-away insert to be attached detachably to the tip portion of a bit on cutting and planing of workpieces such as those of various types of steel and cast iron, drill or miniature drill used in drilling of the workpieces materials, and solid type end mill used in planing, fluting and chamfering of workpieces. There is also known a throw-away end milling tool which is used to cut in the same manner as in the case of the solid type end mill after the throw-away insert was detachably attached.
There is known a coated cemented carbide tool produced by depositing, on the surface of a cemented carbide substrate, a wear-resistant coating layer which is made of one layer or a plurality of two or more layers, among a layer of carbide of Ti (hereinafter referred to as TiC), a layer of nitride of Ti (hereinafter referred to as TiN), a layer of carbonitride of Ti (hereinafter referred to as TiCN), a layer of carboxide of Ti (hereinafter referred to as TiCO) and a layer of carbonitroxide of Ti (hereinafter referred to as TiCNO) and has an average thickness of 1 to 15 μm, using a conventional chemical deposition apparatus. It is also well known that this coated cemented carbide tool may be used in continuous cutting and interrupted cutting of various types of steel and cast iron.
There is also known a coated cemented carbide tool produced by depositing, on the surface of the cemented carbide substrate, a wear-resistant coating layer which is composed of: (a) a lower coating layer which is made of one layer or a plurality of two or more layers, among a layer of carbide of Ti (hereinafter referred to as TiC), a layer of nitride of Ti (hereinafter referred to as TiN), a layer of carbonitride of Ti (hereinafter referred to as TiCN), a layer of carboxide of Ti (hereinafter referred to as TiCO) and a layer of carbonitroxide of Ti (hereinafter referred to as TiCNO), and has an average thickness of 0.5 to 15 μm, deposited using a conventional chemical deposition device; and (b) an upper coating layer which is made of either or both of an aluminum oxide (hereinafter referred to as Al2O3) layer and an Al2O3—ZrO2 mixed layer made of a matrix of Al2O3 and a zirconium oxide (hereinafter referred to as ZrO2) phase dispersed and distributed therein (hereinafter referred to as an Al2O3—ZrO2 mixed layer) described in Japanese Patent Application, First Publication No. Sho 57-39168 and Japanese Patent Application, First Publication No. Sho 61-201778, and has an average thickness of 0.5 to 15 μm, deposited using the same conventional chemical deposition device. It is also known that this coated cemented carbide tool may be used in continuous cutting and interrupted cutting of various types of steel and cast iron.
It is also known that a coated cemented carbide tool is produced by depositing, on the surface of the cemented carbide substrate, a wear-resistant coating layer which is made of a single-layered or multi-layered surface hard layer of either or both of a composite nitride layer of Ti and Al (hereinafter referred to as a (Ti, Al)N layer) and a composite carbonitride layer of Ti and Al (hereinafter referred to as a (Ti, Al)CN layer), which respectively satisfy the composition formula: (Ti1-XAlX)N and the composition formula: (Ti1-XAlX)C1-YNY (wherein X represents 0.15 to 0.65 and Y represents 0.5 to 0.99 in terms of an atomic ratio), and has an average thickness of 0.5 to 15 μm, as described in Japanese Patent Application, First Publication No. Sho 62-56565, using an arc ion plating apparatus as a kind of physical deposition apparatus shown in a schematic explanatory view of FIG. 1 under the conditions that arc discharge is generated between an anode electrode and a cathode electrode (vapor source), in which a Ti—Al alloy with a predetermined composition is set, under the conditions of a voltage of 35 V and a current of 90 A in the state where the atmosphere of the apparatus is evacuated to 0.5 Pa and heated to a temperature of 500° C. using a heater and, at the same time, a nitrogen gas and/or a methane gas, as a reactive gas, are introduced into the apparatus and a bias voltage of −200 V is applied to the cemented carbide substrate.
There is also known a coated cemented carbide tool produced by physically depositing, on the surface of the cemented carbide substrate, a single-layered or multi-layered lower hard layer of a wear-resistant coating layer, which is made of either or both of a composite nitride layer of Ti and Al (hereinafter referred to as a (Ti, Al)N layer) and a composite carbonitride layer of Ti and Al (hereinafter referred to as a (Ti, Al)CN layer), which respectively satisfy the composition formula: (Ti1-XAlX)N and the composition formula: (Ti1-XAlX)C1-YNY (wherein X represents 0.15 to 0.65 and Y represents 0.5 to 0.99 in terms of an atomic ratio), and has an average thickness of 0.5 to 15 μm, as described in Japanese Patent Application, First Publication No. Sho 62-56565, using an arc ion plating apparatus as a kind of physical deposition apparatus shown in a schematic explanatory drawing view of FIG. 1 under the conditions that arc discharge is generated between an anode electrode and a cathode electrode (vapor source), in which a Ti—Al alloy with a predetermined composition is set, under the conditions of a voltage of 35 V and a current of 90 A in the state where the atmosphere of the apparatus is evacuated to 0.5 Pa and heated to a temperature of 500° C. using a heater and, at the same time, a nitrogen gas and/or a methane gas, as a reactive gas, are introduced into the apparatus and a bias voltage of −200 V is applied to the cemented carbide substrate, and further depositing chemically thereon an upper coating layer which is made of either or both of an aluminum oxide (hereinafter referred to as Al2O3) layer and an Al2O3—ZrO2 mixed layer made of a matrix of Al2O3 and a zirconium oxide (hereinafter referred to as ZrO2) phase dispersed and distributed therein (hereinafter referred to as an Al2O3—ZrO2 mixed layer) described in Japanese Patent Application, First Publication No. Sho 57-39168 and Japanese Patent Application, First Publication No. Sho 61-201778, and has an average thickness of 0.5 to 10 μm, using a conventional chemical deposition apparatus. It is also known that this coated cemented carbide tool may be used in continuous cutting and interrupted cutting of various types of steel and cast iron.
Recently, high performance cutting apparatuses have made remarkable advances. With an increase in strong demands of labor saving and energy saving as well as cost reduction to the cutting operation, cutting tools tend to require the versatility that it is hardly influenced by the cutting conditions as small as possible. When a conventional coated cemented carbide tool is used in continuous cutting and interrupted cutting of steel and cast iron under normal conditions, no problems arise. However, when a cutting operation using an end mill or drill whose cutting edge is exposed to interrupted cutting, and an interrupted cutting operation (hereinafter referred to as “interrupted cutting”) using a throw-away insert are conducted under deep cutting conditions such as thick depth-of-cut and high feed, the surface hard layer is liable to be peeled off from the surface of the cemented carbide substrate due to high mechanical and thermal impacts produced during the cutting. Since the primary layer and surface hard layer are very hard, chipping is liable to occur at the cutting edge portion in the interrupted cutting under deep cutting conditions accompanied with high mechanical and thermal impacts, and failure occurs within a relatively short time.